The invention relates to a method for calibrating a roll stand in which for determining the relative pivoted position of the roll set for the adjustment of a symmetrical roll gap and/or for determining the expansion of the roll stand prior to the actual rolling procedure, the roll set is pressed together by a radial force and the resulting deformation of the roll stand is preferably measured on the piston-cylinder unit, wherein the thereby determined pivoted position of the roll set and/or the stand thereby determined modulus (M) during the later rolling of a rolling stock between the work rolls is computationally utilized by the employment of the roll set.
Roll stands are well known in which interacting work rolls are supported by at least two back-up rolls in order to roll, for example, a steel strip. Reference is being made as an example to EP 0 763 391 B1.
For achieving a high quality when rolling a strip in a roll stand, it is required that after an exchange of the rolls of the roll stand a calibration is carried out.
If axial displacement systems are provided for the work rolls (for example, so-called CVC-system), the work rolls are during the calibration in a basic position (axial displacement is zero). During calibration, the work rolls are pressed directly on each other and the expansion curve is recorded, the strand modulus is determined, and the roll gap is adjusted to be parallel or symmetrical. This is taking place prior to the rolling process. During subsequent rolling, the conditions during calibration are simulated with a computer program and converted to the rolling conditions (strip width), and to be able to precisely adjust the strip thickness.
In the process, the following significant observations have been made: The strip width is in most cases significantly narrower than the contact width between the two work rolls. This means that there are different contact conditions during calibrating, on one hand, and during rolling on the other hand. This, in turn, leads to different stand expansions in the two cases mentioned above. Depending on the type of roll used (particularly when CVC-rolls are used), the stand modulus varies in dependence on the relative axial displacement between the work rolls. Moreover, during the axial displacement, the geometric conditions change in the roll gap as well as between the work and back-up rolls. This is especially true when no symmetrical rolls, but only rolls with asymmetrical profiles are used (for example, with CVC-grinding or a similar shape). The work rolls of roll stands with displacement are usually longer by twice the displacement distance than the length of the back-up rolls, or in conventional roll stands without axial displacement, they correspond to the length of the work rolls.